Hitherto, coil components such as an inductor, a transformer, and a choke coil, have been used in various articles such as household electric appliances, industrial equipment, and vehicles. A coil component includes a magnetic core and a coil wound around the magnetic core. In this magnetic core, ferrite, which is excellent in magnetic property, shape flexibility and costs, has widely been used.
In recent years, a decrease in the size of power source devices of electronic instruments and others has been advancing, so that intense desires have been increased for coil components which are small in size and height, and are usable against a large current. As a result, the adoption of powder magnetic cores, in each of which a metallic magnetic powder is used, and which are higher in saturation magnetic flux density than ferrite, has been advancing. Examples of the used metallic magnetic powder include Fe—Si based, and Fe—Ni based magnetic alloy powders. For coil components, the following structures are adopted: an ordinary structure in which a coil is wound around a powder magnetic core obtained by pressure forming; and additionally a structure obtained by pressure-forming a coil and a magnetic powder integrally to satisfy the request of decreasing the coil components in size and height (coil-molded structure).
A powder magnetic core obtained by compacting a magnetic alloy powder of an Fe—Si based, Fe—Ni based, or some other based type is high in saturation magnetic flux density; however, the core is low in electrical resistivity since the powder is an alloy powder. For this reason, a method is used for heightening the insulating property between particles of magnetic alloy powder, for example, a method of forming an insulating coat onto the surface of the alloy powder, and then forming the powder. Patent Document 1 discloses an example using an Fe—Cr—Al based magnetic powder as a magnetic powder enabling a self-production of a high-electrical-resistance material, which is to be an insulating coat. In Patent Document 1, the magnetic powder is subjected to oxidizing treatment to produce an oxidized film having a high electrical resistance onto the surface of the magnetic powder. This magnetic powder is solidified and formed by spark plasma sintering to yield a powder magnetic core.